CN117642657A

CN117642657A - Display with image light turning

Info

Publication number: CN117642657A
Application number: CN202280049951.0A
Authority: CN
Inventors: 朱塞佩·卡拉菲奥雷; 彭枫琳; 耿莹; 亚历山大·科舍列夫; 吕璐; 王梦霏; 雅克·戈利耶
Original assignee: Meta Platforms Technologies LLC
Current assignee: Meta Platforms Technologies LLC
Priority date: 2021-07-16
Filing date: 2022-07-14
Publication date: 2024-03-01
Also published as: US20230017524A1; EP4370955A1; TW202305470A; US11709411B2; WO2023288014A1

Abstract

A display device includes: a directional illuminator that provides a beam of light; a display panel downstream of the directional illuminator, the display panel for receiving and spatially modulating the light beam; and a beam redirection module downstream of the display panel for variably redirecting the spatially modulated light beam. The illumination light is diverted by the beam redirection module such that an exit pupil of the display device can be diverted to match one or more eye positions of the user.

Description

Display with image light turning

Technical Field

The present disclosure relates to optics, and in particular to visual displays and components and modules thereof.

Background

The visual display provides information including still images, video, data, etc. to one or more viewers. Visual displays find application in a variety of fields including entertainment, education, engineering, science, professional training, advertising, to name a few. Some visual displays (e.g., televisions) Display images to multiple users, while some visual Display systems (e.g., near-Eye displays (NED)) are intended for use by individual users.

An artificial reality system typically includes a NED (e.g., in the form of a headset or pair of glasses) configured to present artificial reality content to a user. The near-eye display may display the Virtual object, or combine an image of the real object with the Virtual object, as in a Virtual Reality (VR) application, an augmented Reality (Augmented Reality, AR) application, or a Mixed Reality (MR) application. For example, in an AR system, a user may view both an Image of a virtual object (e.g., a Computer-Generated Image (CGI)) and the surrounding environment through a perspective combiner component. The combiner component of the wearable display is typically transparent to external light, but includes some light routing optics to direct the display light into the field of view of the user.

Head mounted display systems desire compact and energy efficient display devices. Because Head Mounted Displays (HMDs) or NED displays are typically worn on the head of a user, large, heavy, unbalanced and/or heavy display devices with heavy batteries would be cumbersome and uncomfortable for the user to wear. Compact display devices require compact and energy efficient light sources, image projectors, light guides (lightguides), focusing optics, and the like.

Disclosure of Invention

In one aspect of the present invention, there is provided a display device including: a directional illuminator for providing a light beam; a display panel downstream of the directional illuminator for receiving and spatially modulating the light beam to provide a spatially modulated light beam carrying an image in the linear domain; and a beam redirection module downstream of the display panel for variably redirecting the spatially modulated light beam.

The display device may further comprise a visual lens downstream of the beam redirection module for forming an image in an angular domain at an eyebox of the display device from an image in a linear domain carried by the spatially modulated light beam and redirected by the beam redirection module.

The display device may further include: an eye-tracking system for determining a pupil position of the user's eye in the eyebox; and a controller operatively coupled to the eye tracking system and the beam redirection module and configured to cause the beam redirection module to redirect the spatially modulated light beam to match an eye pupil position in the eyebox.

The directional illuminator may comprise a slab single mode waveguide or a slab multimode waveguide.

The directional illuminator may include a pupil replicating light guide.

The beam redirection module may comprise a stack of switchable gratings.

Each switchable grating in the stack may be configured to redirect the spatially modulated light beam at a zero angle in a first state and to redirect the spatially modulated light beam at a predetermined non-zero angle in a second state, wherein the predetermined non-zero angles of the different switchable gratings in the stack may be in a binary relationship to each other.

The stack of switchable gratings may comprise a Pancharatnam-Berry phase (PBP) Liquid Crystal (LC) switchable grating.

The stack of switchable gratings further comprises a switchable polarization rotator disposed downstream of the PBP LC switchable grating and a circular polarizer disposed downstream of the switchable polarization rotator.

The directional illuminator may be configured to provide a beam of light comprising light in a first color channel and a second color channel; the PBP LC switchable grating comprises a first PBP LC switchable grating and a second PBP LC switchable grating; the first PBP LC switchable grating may include a first LC layer having a first optical retardation substantially equal to: an odd number of half wavelengths of the first color channel; and an even number of half wavelengths of the second color channel; and the second PBP LC switchable grating may include a second LC layer having a second optical retardation substantially equal to: an odd number of half wavelengths of the second color channel; and an even number of half wavelengths of the first color channel.

The directional illuminator may be further configured to provide a light beam comprising light in a third color channel; and the PBP LC switchable grating may further include a third PBP LC switchable grating including a third LC layer having a third optical retardation substantially equal to: odd half wavelengths of the third color channel; and an even number of half wavelengths of the first color channel and the second color channel.

In one aspect of the present invention, there is provided a display device including: a light source for providing a light beam; a pupil replication light guide downstream of the light source for expanding the light beam to provide an expanded light beam; a display panel downstream of the pupil replication light guide for receiving and spatially modulating the expanded light beam to provide a spatially modulated light beam carrying an image in the linear domain; and a beam redirection module downstream of the display panel for variably redirecting the spatially modulated light beam.

The display device may further include: a visual lens downstream of the beam redirection module for forming an image in an angular domain at an eye-ward region of the display device from an image in a linear domain carried by the spatially modulated light beam; an eye-tracking system for determining an eye pupil position of the display user in the eyebox; and a controller operatively coupled to the eye tracking system and the beam redirection module and configured to cause the beam redirection module to redirect the spatially modulated light beam to match an eye pupil position in the eyebox.

The beam redirection module may comprise a stack of switchable gratings.

The PBP LC switchable grating may include an LC layer between a plurality of parallel substrates configured to apply an electric field across the LC layer, wherein LC molecules in the LC layer may be oriented substantially parallel to the substrates in the absence of the electric field and substantially perpendicular to the substrates in the presence of the electric field.

In one aspect of the invention, there is provided a method for displaying an image to a user, the method comprising: providing a light beam; receiving and spatially modulating the light beam to provide a spatially modulated light beam carrying an image in the linear domain; and using a beam redirection module to variably redirect the spatially modulated light beam toward the user's eye.

The method may further comprise: an image in the angular domain is formed by a vision lens from an image in the linear domain carried by the spatially modulated light beam and redirected by the beam redirection module.

The method may further comprise: determining an eye pupil position of the display user in the eyebox; and causing the beam redirection module to redirect the spatially modulated light beam to match an eye pupil position in the eyebox.

Using the beam redirection module may include switching at least one switchable grating in a stack of switchable gratings.

Drawings

Exemplary embodiments will now be described in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a near-eye display device of the present disclosure;

FIG. 2 is a side cross-sectional view of a directional illuminator for the display device of FIG. 1, the directional illuminator including a pupil replicating light guide;

FIG. 3A is a front view of an active Panchatam-Berry phase (PBP) Liquid Crystal (LC) grating that may be used in a beam redirection module of the display device of FIG. 1;

FIG. 3B is an enlarged schematic view of LC molecules in the LC layer of the active PBP LC grating of FIG. 3A;

FIGS. 4A and 4B are schematic side views of the active PBP LC grating of FIGS. 3A and 3B in the beam-redirecting module of FIG. 1, showing light propagation in the off state (FIG. 4A) and on state (FIG. 4B) of the active PBP LC grating;

FIG. 5 is a schematic side view of an optical subassembly including the active PBP LC grating and switchable waveplates of FIG. 3A and FIGS. 4A and 4B, the stack being capable of switching an incident light beam between three different propagation directions;

fig. 6 is an exploded view of an embodiment of the beam redirection module of fig. 1, comprising a binary stack of the optical sub-assemblies of fig. 5.

Fig. 7A and 7B are schematic side views of a multi-color switchable PBP LC grating assembly in a diffracted state (fig. 7A) and in a non-diffracted state (fig. 7B).

FIG. 8 is a schematic diagram of a near-eye display device of the present disclosure having a transmissive display panel;

FIG. 9 is a schematic diagram of a near-eye display device of the present disclosure having a reflective display panel;

FIG. 10 is an enlarged view of the near-eye display device of FIG. 9, illustrating propagation of a polarized light beam;

FIG. 11 is a side cross-sectional view of a directional illuminator for the display device of FIG. 1, the directional illuminator comprising a slab single mode waveguide or a few mode waveguide;

FIG. 12 is a view of a near-eye display of the present disclosure having the form factor of a pair of eyeglasses;

FIG. 13 is a flow chart of a method of the present disclosure for displaying an image to a user;

fig. 14 is a three-dimensional view of a head mounted display of the present disclosure.

Detailed Description

While the present teachings are described in connection with various embodiments and examples, it is not intended to limit the present teachings to those embodiments. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those of skill in the art. All statements herein reciting principles, aspects, and embodiments of the disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Furthermore, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

As used herein, the terms "first" and "second," etc. are not intended to imply a sequential order, but rather to distinguish one element from another element unless otherwise explicitly stated. Similarly, the sequential order of the method steps does not imply a sequential order of their execution unless explicitly stated. In fig. 1, 2, 8 to 10 and 12, like reference numerals denote like elements.

A display device provides image light carrying an image for viewing by a user. The image light may be dispersed over a large area including all possible locations of one or more display viewers. Dispersing the image light over a wide area causes the user to lose a large portion of the light. According to the present disclosure, by having the exit pupil of the display follow the pupil position of the eye, image light may be specifically delivered to the eye region of the user, or even to the pupil of the eye. To achieve the pupil steering function, a directional illuminator is used to illuminate the display panel. The display panel spatially modulates the illumination light. The spatially modulated light is directed by a beam redirection module arranged in the light path downstream of the display panel. Such a configuration can improve image brightness and/or save power by not transmitting image light to an unobservable area.

According to the present disclosure, there is provided a display device including: a directional illuminator for providing a light beam; a display panel downstream of the directional illuminator for receiving and spatially modulating the light beam to provide a spatially modulated light beam carrying an image in the linear domain; and a beam redirection module downstream of the display panel for variably redirecting the spatially modulated light beam. Downstream of the beam redirection module may be provided a visual lens for forming an image in an angular domain at an eyebox (eyebox) of the display device from an image in a linear domain carried by the spatially modulated light beam and redirected by the beam redirection module. An eye tracking system may be provided to determine the user's eye pupil position in the eyebox. A controller may be operably coupled to the eye tracking system and the beam redirection module and configured to cause the beam redirection module to redirect the spatially modulated light beam to match an eye pupil position in the eyebox. The directional illuminator may comprise at least one of a slab single mode waveguide, a slab few mode waveguide, or a pupil replicating light guide.

In some embodiments, the beam redirection module comprises a stack of switchable gratings. Each switchable grating in the stack may be configured to redirect the spatially modulated light beam at a zero angle in the first state and to redirect the spatially modulated light beam at a predetermined non-zero angle in the second state. The predetermined non-zero angles of the different switchable gratings in the stack may be in a binary relationship with each other. The stack of switchable gratings may comprise, for example, a Pancharatnam-Berry phase (PBP) Liquid Crystal (LC) switchable grating. The stack of switchable gratings may further comprise a switchable polarization rotator disposed downstream of the PBP LC switchable grating and a circular polarizer disposed downstream of the switchable polarization rotator.

In embodiments where the directional illuminator is configured to provide a beam of light comprising a first color channel and a second color channel, the PBP LC switchable grating may comprise a first PBP LC switchable grating and a second PBP LC switchable grating. The first PBP LC switchable grating may include a first LC layer having a first optical retardation substantially equal to an odd number of half wavelengths of the first color channel and an even number of half wavelengths of the second color channel. The second PBP LC switchable grating may include a second LC layer having a second optical retardation substantially equal to an odd number of half wavelengths of the second color channel and an even number of half wavelengths of the first color channel. More color channels may be provided. For example, the directional illuminator may be further configured to provide a light beam comprising light located in the third color channel. The PBP LC switchable gratings may include a third PBP LC switchable grating including a third LC layer having a third optical retardation substantially equal to an odd number of half wavelengths of the third color channel and an even number of half wavelengths of the first and second color channels.

According to the present disclosure, there is provided a display device including: a light source for providing a light beam; a pupil replication light guide downstream of the light source for expanding the light beam to provide an expanded light beam; a display panel downstream of the pupil replication light guide for receiving and spatially modulating the expanded light beam to provide a spatially modulated light beam carrying an image in the linear domain; and a beam redirection module downstream of the display panel for variably redirecting the spatially modulated light beam. Downstream of the beam redirection module, a visual lens may be provided for forming an image in an angular domain at an eyebox of the display device from an image in a linear domain carried by the spatially modulated light beam. An eye tracking system may be provided for determining an eye pupil position of a display user in the eyebox. A controller may be operably coupled to the eye-tracking system and the beam-redirecting module and configured to cause the beam-redirecting module to redirect the spatially modulated light beam to match an eye pupil position in the eyebox. The beam redirection module may comprise a stack of switchable gratings, for example PBP LC switchable gratings. The PBPLC switchable grating may include an LC layer between parallel substrates configured to apply an electric field across the LC layer. In the absence of an electric field, LC molecules in the LC layer may be oriented substantially parallel to these substrates; in the presence of an electric field, LC molecules in the LC layer may be oriented substantially perpendicular to the substrates.

In accordance with the present disclosure, there is also provided a method for displaying an image to a user. The method comprises the following steps: providing a light beam; receiving and spatially modulating the light beam to provide a spatially modulated light beam carrying an image in the linear domain; and variably redirecting the spatially modulated light beam toward the user's eye using a beam redirection module. The method may include forming, by a vision lens, an image in an angular domain from an image in a linear domain carried by the spatially modulated light beam and redirected by the beam redirection module. The method may further include determining an eye pupil position of the display user in the eyebox, and causing the beam redirection module to redirect the spatially modulated light beam to match the eye pupil position in the eyebox. Using the beam redirection module may include switching at least one switchable grating in a stack of switchable gratings.

Fig. 1 shows an illustrative general construction of a display device with exit pupil steering (scheduling). Display device 130 includes directional illuminator 100 that provides an illumination beam 114. Herein, the term "directional luminaire" refers to a luminaire that provides a directional light beam, rather than a diffuse light beam (obtained by passing the light beam through a diffuser such as opal glass). The directed beam may be a parallel beam or a beam with well-defined divergence or convergence. Illustrative examples of directional illuminators are provided further below.

A display panel 118 is disposed in the light path downstream of directional illuminator 100. For example, the display panel may include a light valve array, such as a liquid crystal array. The display panel 118 receives the light beam 114 and spatially modulates the light beam in amplitude and/or phase to provide a spatially modulated light beam 115 that carries an image in the linear domain. In this context, the term "image in the linear domain" refers to an image in which different coordinates of the light rays carrying the image correspond to different pixels of the image, while the term "image in the angular domain" refers to an image in which different angles of the light rays carrying the image correspond to different pixels. In this context, the term "pixel" refers to an element of a displayed image.

The beam redirection module 150 is disposed downstream of the display panel 118. The function of beam redirection module 150 is to variably redirect spatially modulated light beam 115 to match the position of user's eye 134 or, in some embodiments, to match a particular position of pupil 135 of eye 134. In fig. 1, three such positions are shown: "A", "B" and "C". Beam redirection module 150 is capable of redirecting spatially modulated light beam 115 to any of locations A, B or C, or any location therebetween, if desired. Note that positions "a", "B" and "C" are typically located in three-dimensional space downstream of beam redirection module 150.

Turning to fig. 2, a multi-mode directional illuminator 200 may be used as the directional illuminator 100 in the display device 130 of fig. 1. The directional illuminator 200 of fig. 2 includes a pupil replication light guide 206 configured to receive the light beam 204 from the light source 202. Pupil replication light guide 206 includes opposing first and second surfaces 211, 212 that extend parallel to each other. The light beam 204 is coupled into the pupil replication light guide 206 by a coupler 208 to propagate in the pupil replication light guide 206 by a series of meandering reflections (e.g. total internal reflection or TIR from opposite first and second surfaces 211, 212, i.e. parallel to the Y-axis in the downward direction in fig. 2). The output beam (also referred to as an expanded beam) of the multimode directional illuminator 200 includes parallel beam portions 214 offset along the Y-axis, which are coupled out of the pupil replication light guide 206 by a coupler 216. More than one grating 216 may be provided. For example, the coupler 208 and/or the coupler 216 may include a diffraction grating. The spacing of the diffraction gratings may be selected to provide a desired angular deflection for beam in-coupling and out-coupling of the beam. The gratings may include surface relief gratings, refractive transmission gratings, volume bragg gratings, volume holographic gratings, polarization holographic gratings, and the like. These gratings may be polarization selective to diffract light only in a particular polarization state, e.g., linear polarization of a particular orientation or circular polarization of a particular handedness (handedness).

Referring to fig. 3a, a pancharatnam-Berry phase (PBP) Liquid Crystal (LC) switchable grating 300 may be used as a building block for beam redirection module 150 of display device 130 of fig. 1. The PBP LC switchable grating 300 includes LC molecules 302 in an LC layer 304. LC molecules 302 are disposed in the XY plane at different in-plane orientations according to the X coordinate. The orientation angle phi (x) of the LC molecules 302 in the PBP LC switchable grating 300 is given by:

φ(x)＝πx/T＝πx sinθ/λ _o (1)

wherein lambda is _o Is the wavelength of the incident light, T is the pitch of the PBP LC switchable grating 300, and θ is the diffraction angle given by:

θ＝sin ^-1 (λ _o /T) (2)

the azimuth angle phi varies continuously over the surface of the LC layer 304 parallel to the XY plane shown in fig. 3B. The variation has a constant period equal to T.The optical phase retardation P in the PBP LC grating 300 of fig. 3A is due to the PBP effect when the optical retardation R of the LC layer 304 is equal to λ _□ At/2, this effect appears to be P (x) =2Φ (x).

Fig. 4A and 4B illustrate the operation of the PBP LC switchable grating 300 of fig. 3A. The PBP LC switchable grating 300 includes an LC layer 304 (fig. 3A) disposed between a plurality of parallel substrates configured to apply an electric field across the LC layer 304. In the absence of an electric field, LC molecules 302 are substantially parallel to these substrates; LC molecules 302 are substantially perpendicular to these substrates in the presence of an electric field.

In fig. 4A, the PBP LC switchable grating 300 is in an off state such that its LC molecules 302 are arranged mainly parallel to the substrate plane, i.e. parallel to the XY plane in fig. 4A. When the incident light beam 415 is left-hand circularly polarized (LCP), the PBP LC switchable grating 300 redirects the light beam 415 upward at a predetermined non-zero angle, and the light beam 415 becomes right-hand circularly polarized (RCP). The RCP deflected beam 415 is shown in solid lines. When the incident beam 415 is right-hand circularly polarized (RCP), the PBP LC switchable grating 300 redirects the beam 415 downward at a predetermined non-zero angle, with the beam 415 becoming left-hand circularly polarized (LCP). The LCP deflected beam 415 is shown in dashed lines. As shown in fig. 4B, a voltage V is applied to the PBP LC switchable grating 300 to reorient LC molecules along the Z-axis perpendicular to the substrate plane. At this orientation of LC molecules 302, the PBP structure is cleared and beam 415 retains its original orientation, whether it be LCP or RCP. Thus, the active PBP LC grating 400 has variable beam steering characteristics.

In accordance with the present disclosure, the active PBP LC grating described above may be used to construct a beam deflection element that is switchable between three beam deflection angles. Referring to fig. 5, a beam deflecting element 500 includes the PBP LC switchable grating 300 of fig. 3A and fig. 4A and 4B, an LC switchable half-wave plate 502 serving as a switchable polarization rotator, and a left-handed circular polarizer 503 arranged as a stack. In this example, the PBP LC switchable grating 300 comprises a positive LC material, i.e. an LC material showing positive dielectric anisotropy, but a negative LC material may also be used. The input light may be unpolarized, i.e., the input light may include both LCP light and RCP light. When the PBP LC switchable grating 300 is in the "on" state, i.e., when an electric field is applied, the PBP structure is cleared, so the PBP LC switchable grating 300 does not deflect the light beam; as shown at 511, no overall beam deflection occurs. When the PBP LC switchable grating 300 is in the "off" state, i.e., when no electric field is applied, PBP LC orientation occurs, providing an angular beam deflection of α for LCP light and an angular beam deflection of- α for RCP light. When the switchable half-wave plate 502 is in the off state, i.e. when no electric field is applied, there is a half-wave retardation, as shown at 512. As a result, the RCP light at the deflection angle- α becomes LCP light, which passes through the left-handed circular polarizer 503. Thus, the beam-deflecting element 500 deflects the light beam by an angle- α. When switchable half-wave plate 502 is in the on state, i.e., when an electric field is applied, the half-wave retardation is cleared and the LCP light remains L polarized, as shown at 513. Thus, the beam-deflecting element 500 deflects the light beam by an angle α.

According to one aspect of the present disclosure, beam redirection module 150 of display device 130 of fig. 1 may include a stack of beam deflection elements 500 of fig. 5 with varying degrees of deflection. The magnitudes of the deflections may be in a binary relationship with each other. Referring to fig. 6, as a non-limiting illustrative example, a binary stack 600 of switchable deflection elements includes: a first switchable deflection element 601 providing a switchable deflection between- α, 0, +α angles; a second switchable deflection element 602 that provides switchable deflection between-2α, 0, +2α angles; a third switchable deflection element 603 that provides switchable deflection between-4α, 0, +4α angles; and a fourth switchable deflection element 604 that provides switchable deflection between-8α, 0, +8α angles. At the same time, switchable deflecting elements 601 to 604 of stack 600 may deflect light beam 606 from the angular range of-15 a to 15 a by switching on and off the respective PBP LC gratings and wave plates.

PBP LC devices may exhibit wavelength dependent performance. From (1) andas can be seen from equation (2), a PBP LC grating with an LC director profile φ (r) will exhibit a wavelength λ ₀ Proportional deflection angle θ. If such a grating is used to redirect the light of a color display, which typically has three primary color channels, only one color channel will be properly redirected.

To ensure that all three color channels are properly redirected, a stack of three PBP LC gratings may be used, one for each color channel. As a non-limiting example, referring to fig. 7A, switchable PBP LC device 700 is a combination of three switchable PBP LC stacks 600 in fig. 6: g stack 701 for green, B stack 702 for blue, and R stack 703 for red. In fig. 7A, the green beam component 711 (solid line) of beam 706 is redirected only by G stack 701; the blue beam component 712 (dashed line) is focused only by the B stack 702; the red beam component 713 (dashed long-dashed line) is focused only by the R stack 703. To provide zero optical power at the wavelengths of the other color channels, the R, G, bpbp LC grating and waveplate thicknesses are selected such that their optical retardation at the two other wavelengths is an integer number of wavelengths or even an even number of half wavelengths, such that the PBP is zero and there is no LCP/RCP polarization transformation, and accordingly the deflection angle at the other two color channels is zero. To provide beam deflection power at the R, G, B channel wavelength, the R, G, bpbp LC grating and waveplate thicknesses are selected such that their optical retardation at their own wavelengths is an odd number of half wavelengths, such that PBP is non-zero and there is LCP/RCP polarization conversion, with the power of the R, G, B grating being non-zero accordingly. This technique can be used to run the PBP LC grating in at least two channels. The PBP LC switchable grating may include a first PBP LC switchable grating and a second PBP LC switchable grating for both color channels. The first PBP LC switchable grating may include a first LC layer having a first optical retardation substantially equal to: an odd number of half wavelengths of the first color channel; and an even number of half wavelengths of the second color channel. The second PBP LC switchable grating may include a second LC layer having a second optical retardation substantially equal to: an odd number of half wavelengths of the second color channel; and an even number of half wavelengths of the first color channel. In a similar manner, the PBP LC switchable grating may further comprise a third PBP LC switchable grating having a third LC layer with a third optical retardation substantially equal to that of the third LC layer for the three color channels: odd half wavelengths of the third color channel; and an even number of half wavelengths of the first color channel and the second color channel.

Referring to fig. 7B, all three stacks 701-603 are in an "on" state, and therefore, the beam deflection power of switchable LC PBP device 700 is zero, i.e., beam 706 remains in the original propagation direction. It should be noted that even though one voltage V is shown applied to the stacks of PBP LC stacks 701 to 603 for simplicity, in a practical embodiment, different voltage sets are typically applied to the different PBP LC stacks 701 to 703. It should also be understood that the term "achromatic" as used herein means that the performance of the PBP LC device is reduced in dependence on wavelength, which achromatism may be incomplete due to the wavelength dependence of the optical retardation within the channel.

The above example of a PBP LC switchable grating only considers the deflection of the beam in one plane. To achieve deflection of the light beam in two orthogonal planes, two PBP LC gratings or two stacks of such gratings may be arranged at a clock angle of 90 degrees with respect to each other. For example, for azimuth angle phi ₁ Each PBP LC switchable grating 300 (fig. 3A) that varies along the X-axis, the stack may include an azimuth angle phi ₂ Along the Y-axis (phi) ₂ PBP LC switchable grating 300 =Φ (y)).

Referring to fig. 8, a transmissive near-eye display (NED) device 830 is an embodiment of the display device 130 of fig. 1. The transmissive NED 830 of fig. 8 uses the transmissive display panel 118, the multimode directional illuminator 200 of fig. 2, and the achromatic switchable PBP LC device 700 of fig. 7A and 7B as a beam redirecting device. Other types of directional illuminators and beam redirecting devices may also be used. The display device 830 also includes a visual lens (oculars) 832 and an eye tracking system 838.

The directional illuminator 200 illuminates the display panel 118 with a beam portion 214 acquired from a beam 204 emitted by a light source 202 and coupled into a pupil replication light guide 206, which outputs the beam portion 214 as explained above. A visual lens 832 is coupled to the display panel 118 for converting an image in the linear domain displayed by the display panel 118 into an image in the angular domain for viewing by the user's eye 834 disposed at the eyebox 836. In this example, the display panel 118 operates in a transmissive mode (transmission).

The eye tracking system 838 is configured to determine the position/orientation of the eye 834 and/or the position of the pupil 835 of the eye 834. A controller 840 is operably coupled to the switchable PBP LC device 700 and the eye tracking system 838 and is configured to adjust the out-coupling angle of the beam portion 214 for the converging beam 817 focused by the ocular lens 832 to match the position of the pupil 835 of the eye. For example, when the eye 834 moves to a new position shown in phantom at 834A, the eye tracking system 838 determines the new position and reports the new position to the controller 840, which then adjusts the switchable PBP LC device 700 to provide the deflected beam portion 214A which is focused by the vision lens 832 to provide the focused beam 817A which is focused at the new position 834A. Such a configuration enables NED 830 to transmit image light only where the pupil of the eye is located, thereby providing energy savings and/or increasing perceived brightness of the viewed image. In other words, NED 830 enables steering of the exit pupil of the display to match the current pupil position of the eye.

The reflective construction of the display device may be realized with, for example, a reflective display panel, such as a reflective liquid crystal on silicon (Liquid Crystal on Silicon, LCoS) display panel. The LCoS display panel combines the possibility of miniaturization with the convenience of providing the drive circuitry on the reflective silicon substrate of the LC array. Referring to fig. 9, a reflective NED 930 is similar to the transmissive NED 830 of fig. 8, but uses a polarized light source 902 and a reflective display panel 918 in place of the transmissive display panel 118. The reflective NED 930 includes a pupil replication light guide 906 having an in-coupling grating 908 and an out-coupling polarization selection grating 916. The polarized light beam 904 emitted by the polarized light source 902 is coupled into the pupil replication light guide 906 through the coupling-in grating 908 and is coupled out as polarized light beam portion 914 by the coupling-out polarization-selective grating 916. Polarized light beam portion 914 is directed to reflective display panel 918, propagates back through pupil replication light guide 906, propagates through switchable PBP LC device 700, and propagates towards viewing lens 832, forming converging beam 917 at eye-ward region 836.

The propagation of beam portion 914 is shown more precisely in fig. 10. The polarized portion 914 of the light beam 904 guided by the pupil replication light guide 906 is coupled out by the polarization-selective grating 916 at a linear polarization perpendicular to the plane of fig. 10 (i.e. parallel to the X-axis). Polarized light beam portion 914 propagates toward reflective display panel 918 (e.g., an LCoS reflective display panel) which reflects light beam portion 914 to propagate back toward pupil replication light guide 906 in a spatially varying polarization state. The portion of light beam 914 in the linear polarization state in the plane of fig. 10 (i.e., parallel to the Y-axis) is free to propagate through the polarization-selective grating 916, while the portion of light beam 914 in the initial polarization state (i.e., perpendicular to the plane of fig. 5 or parallel to the X-axis) is deflected (diffracted) away from the optical path by the polarization-selective grating 916. As a result, the polarized beam portion 914 (left to right in fig. 5, i.e., in the Z-axis direction) propagating through the polarization-selective grating 916 is modulated in amplitude, providing an image in the linear domain. Beam portion 914 may then be redirected by switchable PBP LC device 700 or more generally beam redirection module 150.

Referring now to fig. 11, a single mode directional illuminator 1100 may be used as the directional illuminator 100 of the display device 130 of fig. 1, or as an alternative to the directional illuminator 200 of the display device 830 of fig. 8, for example. The single mode directional illuminator 1100 includes a slab waveguide 1101, typically a single mode slab waveguide or a few mode slab waveguide, and a light source 1102 that provides a light beam 1110 that is coupled into the slab waveguide 1101 using a suitable coupler (e.g., a lens-based coupler, not shown). Slab waveguide 1101 includes a substrate 1104, a (slab) core 1106 disposed on substrate 1104, and a cladding 1108 disposed on core 1106. The thickness of the cover layer 1108 may vary in the direction in which the light 1110 propagates in the core layer 1106 (i.e., along the Y-axis in fig. 11), i.e., may vary spatially. Light 1110 propagates in the Y-direction in fig. 11, and this thickness (measured in the Z-direction) gradually decreases along the Y-direction (i.e., from bottom to top in fig. 11).

A light extractor 1112 (e.g., a thin prism) is disposed on top of the cover 1108. Refractive index n of light extractor 11212 _{Extraction of} Effective refractive index n of propagation mode of specific light 1110 in slab waveguide 1101 _{Effective and effective} Higher and the cover layer 1108 is thin enough to evanescently couple light 1110 out of the core layer 1106 into the light extractor 1112. Illustratively, the thickness of the cover layer 1108 may be between 0.3 microns and 3 microns, or may even be between 0.1 microns and 5 microns in some embodiments.

In operation, light 1110 propagates in the Y direction in core 1106 as indicated by the gray arrows. As light 1110 propagates in core 1106, portions 1116 of light 1110 are coupled out into light extractor 1112. The angle θ (relative to the waveguide normal) at which the plurality of sections 1116 are coupled out depends only on the effective index n of the waveguide mode _{Effective and effective} Refractive index n of the extractor 1112 _{Extraction of} Is defined by the ratio of:

θ＝asin(n _{effective and effective} /n _{Extraction of} ) (3)

Equation (3) follows the law of momentum transfer applicable to light. The rate of light tunneling is controlled by the thickness of the cover layer 1108.

The thickness of the cover layer 1108 may decrease in the direction of propagation of the light 1110 (i.e., along the Y-axis) to offset the consumed optical power level of the light 1110 as the plurality of portions 1116 evanescently couple out, thereby increasing the spatial uniformity of the collimated light 1114 that is coupled out of the core layer 1106, through the top cover layer 1108, and into the light extractors 1112. The wedge shape may be achieved by a low resolution grey scale etching technique. An AR coating may be present between the cover 1108 and the light extractors 1112. Depending on the refractive indices of the light extractors 1112, the cover layer 1108, and the bonding material used, an AR coating may be applied to the top of the cover layer 1108, the bottom of the light extractors 1112, or both.

In the illustrated embodiment, the light extractors 1112 are thin prisms, e.g., less than 1mm, having first face 1121 and second face 1122 that form a small acute angle. The second face 1122 may include a reflector, such as a metal or dielectric reflector, for reflecting the portion 1116 of light coupled out by the prism to propagate back through the slab waveguide 1101 at an angle near normal. For example, for a 0.95mm high light extractor 212, the angle may be about 26 degrees; for some materials, the angle may be as low as within 15 degrees of the normal angle. In some embodiments, the reflector at the second side 1122 may be polarization selective. In applications requiring a wider beam, a thicker prism may be used. In this case, the height of the prism may still be less than half the beam diameter. The second face 1122 may be polished to have a radius of curvature such that the reflector has optical (i.e., in-focus or out-of-focus) power. Note that the term "prism" as used herein includes prisms having curved outer faces.

Turning to fig. 12, an Augmented Reality (AR) near-eye display 1200 includes a frame 1201 that supports for each eye: a light source 1202; a pupil replication light guide 1206 as disclosed herein for guiding the light beam into the interior and coupling out portions of the light beam; a display panel 1218 illuminated by the beam portion coupled out of the pupil replication light guide 1206 for spatially modulating the beam portion; a beam redirection module 1250 for redirecting the spatially modulated beam portion; a visual lens 1232 for converting an image in the linear domain displayed by the display panel 1218 into an image in the angular domain at the eyebox 1236 as disclosed herein; eye tracking camera 1238; and a plurality of eyebox illuminators 1262 shown as black dots. The eyebox illuminator 1262 may be supported by the visual lens 1232 for illuminating the eyebox 1236.

The purpose of eye-tracking camera 1238 is to determine the position and/or orientation of the user's eyes to enable steering of the output image light to the position of the user's eyes, as disclosed herein. The illuminator 1262 illuminates the eye at the respective eyebox 1236 to enable the eye tracking camera 1238 to acquire images of the eye and provide reference reflection, i.e., glints. The glints may be used as reference points in the acquired eye images, facilitating the determination of the eye gaze direction by determining the position of the eye pupil image relative to the glint image. To avoid distracting the user's light from the eyebox illuminator 1262, the light illuminating the eyebox 1236 may be made invisible to the user. For example, infrared light may be used to illuminate the eyebox 1236.

Referring now to FIG. 13, and also to FIGS. 1, 2, and 8, a method 1300 for displaying an image to a user includes providing (1302) a light beam, e.g., light beam 204 emitted by light source 202 (FIG. 2), receiving and spatially modulating (FIG. 13; 1304) the light beam to provide a spatially modulated light beam (e.g., modulated light beam 115 in FIG. 1) carrying an image in a linear domain, and using a beam redirection module, such as beam redirection module 150 or switchable PBP LC device 700, to variably redirect the spatially modulated light beam toward an eye of the user (FIG. 13; 1306).

The method 300 may further include forming (1307) an image in the angular domain from an image in the linear domain carried by the spatially modulated light beam and redirected by the beam redirection module by a visual lens (e.g., visual lens 832 shown in fig. 8). A further optional step of method 300 may include determining (1305) an eye pupil position of the user in the eyebox to match the eye pupil position in the eyebox prior to redirecting (1306) the spatially modulated light beam. Using the beam redirection module may include switching at least one switchable grating (e.g., PBP LC grating 300 of fig. 3) in a stack of switchable gratings (e.g., stack 600 of fig. 6).

Turning to fig. 14, hmd 1400 is an example of an AR/VR wearable display system that encloses a user's face to provide a greater degree of immersion for the user in an AR/VR environment. HMD 1400 may generate a fully virtual 3D image. HMD 1400 may include a front body 1402 and a belt 1404 that may be secured around a user's head. The front body 1402 is configured for placement in front of the eyes of a user in a reliable and comfortable manner. A display system 1480 may be provided in the front body 1402 for presenting AR/VR images to a user. The display system 1480 may include any of the display devices and illuminators disclosed herein. The side 1406 of the front body 1402 may be opaque or transparent.

In some embodiments, the front body 1402 includes a positioner 1408 and an inertial measurement unit (Inertial Measurement Unit, IMU) 1410 for tracking acceleration of the HMD 1400, and a position sensor 1412 for tracking a position of the HMD 1400. The IMU 1410 is an electronic device that generates data representing a position of the HMD 1400 based on received measurement signals from one or more of the plurality of sensors 1412 that generate one or more measurement signals in response to motion of the HMD 1400. Examples of the position sensor 1412 include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor for error correction of the IMU 1410, or some combination thereof. The position sensor 1412 may be located external to the IMU 1410, internal to the IMU 1410, or some combination thereof.

The locator 1408 is tracked by an external imaging device of the virtual reality system so that the virtual reality system can track the position and orientation of the entire HMD 1400. The information generated by the IMU 1410 and the position sensor 1412 may be compared to the position and orientation acquired by the tracking locator 1408 to improve the tracking accuracy of the position and orientation of the HMD 1400. As the user moves and rotates in 3D space, the exact position and orientation is important for presenting the user with the proper virtual scene.

The HMD 1400 may also include a depth camera assembly (Depth Camera Assembly, DCA) 1411 that collects data describing depth information for local areas around some or all portions of the HMD 1400. This depth information may be compared to information from IMU 1410 to more accurately determine the position and orientation of HMD 1400 in 3D space.

HMD 1400 may also include an eye tracking system 1414 for determining the orientation and position of a user's eyes in real-time. The acquired position and orientation of the eyes also allows the HMD 1400 to determine the gaze direction of the user and adjust the image generated by the display system 1480 accordingly. The display system 1480 may be adjusted using the determined gaze direction and convergence angle to reduce convergence adjustment conflicts. As disclosed herein, direction and convergence may also be used for exit pupil steering of a display. Further, the determined focus and gaze angle may be used to interact with a user, highlight an object, bring an object to the foreground, create additional objects or pointers, and so forth. An audio system may also be provided, including, for example, a set of small speakers built into the front body 1402.

Embodiments of the present disclosure may include or be implemented in conjunction with an artificial reality system. The artificial reality system adjusts sensory information (e.g., visual information, audio, touch (somatosensory) information, acceleration, balance, etc.) about the outside, acquired through sensing, in some way before being presented to the user. As non-limiting examples, artificial Reality may include Virtual Reality (VR), augmented Reality (AR), mixed Reality (MR), mixed Reality (Hybrid Reality), or some combination and/or derivative thereof. The artificial reality content may include entirely generated content or generated content combined with collected (e.g., real world) content. The artificial reality content may include video, audio, somatic feedback or haptic feedback, or some combination thereof. Any of these content may be presented in a single channel or in a multi-channel (e.g., in a stereoscopic video that produces a three-dimensional effect to the viewer). Further, in some embodiments, the artificial reality may also be associated with an application, product, accessory, service, or some combination thereof, for creating content in the artificial reality and/or otherwise for use in the artificial reality (e.g., performing an activity in the artificial reality), for example. The artificial reality system providing artificial reality content may be implemented on a variety of platforms including a wearable display (e.g., an HMD connected to a host computer system), a stand-alone HMD, a near-eye display with a form factor of glasses, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

The scope of the present disclosure is not limited by the specific embodiments described herein. Indeed, various embodiments and modifications other than those described herein will be apparent to those skilled in the art from the foregoing description and accompanying drawings. Accordingly, such other embodiments and modifications are intended to fall within the scope of this disclosure. Furthermore, although the present disclosure is described herein in the context of particular embodiments in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that the utility of the present disclosure is not so limited and that the present disclosure may be advantageously implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.

Claims

1. A display device, the display device comprising:

a directional illuminator for providing a beam of light;

a display panel downstream of the directional illuminator for receiving and spatially modulating the light beam to provide a spatially modulated light beam carrying an image in the linear domain; and

A beam redirection module downstream of the display panel for variably redirecting the spatially modulated light beam.

2. The display device of claim 1, further comprising a visual lens downstream of the beam redirection module for forming an image in an angular domain at an eye-ward region of the display device from an image in a linear domain carried by the spatially modulated light beam and redirected by the beam redirection module.

3. The display device of claim 2, the display device further comprising:

an eye-tracking system for determining a pupil position of a user's eye in the eyebox; and

a controller operatively coupled to the eye-tracking system and the beam-redirecting module and configured to cause the beam-redirecting module to redirect the spatially modulated light beam to match the eye pupil position in the eyebox.

4. The display device of claim 1, wherein the directional illuminator comprises a slab single mode waveguide or a slab few mode waveguide.

5. The display device of claim 1, wherein the directional illuminator comprises a pupil replicating light guide.

6. The display device of claim 1, wherein the beam redirection module comprises a stack of switchable gratings, optionally,

wherein each switchable grating in the stack is configured to redirect the spatially modulated light beam at a zero angle in a first state and to redirect the spatially modulated light beam at a predetermined non-zero angle in a second state, wherein the predetermined non-zero angles of the different switchable gratings in the stack are in a binary relationship to each other.

7. The display device of claim 6, wherein the stack of switchable gratings comprises a Pancharatnam-Berry phase (PBP) Liquid Crystal (LC) switchable grating; alternatively, the process may be carried out in a single-stage,

wherein the stack of switchable gratings further comprises a switchable polarization rotator disposed downstream of the PBP LC switchable grating and a circular polarizer disposed downstream of the switchable polarization rotator.

8. The display device of claim 7, wherein,

the directional illuminator is configured to provide the light beam comprising light in a first color channel and a second color channel;

The PBP LC switchable grating comprises a first PBP LC switchable grating and a second PBP LC switchable grating;

the first PBP LC switchable grating includes a first LC layer having a first optical retardation substantially equal to: an odd number of half wavelengths of the first color channel; and an even number of half wavelengths of the second color channel; and is also provided with

The second PBP LC switchable grating includes a second LC layer having a second optical retardation substantially equal to: an odd number of half wavelengths of the second color channel; and an even number of half wavelengths of the first color channel.

9. The display device of claim 8, wherein,

the directional illuminator is further configured to provide the light beam comprising light in a third color channel; and is also provided with

The PBP LC switchable grating further includes a third PBP LC switchable grating including a third LC layer having a third optical retardation substantially equal to: an odd number of half wavelengths of the third color channel; and an even number of half wavelengths of the first color channel and the second color channel.

10. A display device, the display device comprising:

A light source for providing a light beam;

a pupil replication light guide downstream of the light source for expanding the light beam to provide an expanded light beam;

a display panel downstream of the pupil replication light guide for receiving and spatially modulating the expanded light beam to provide a spatially modulated light beam carrying an image in the linear domain; and

11. The display device of claim 10, the display device further comprising:

a visual lens located downstream of the beam redirection module for forming an image in an angular domain at an eye-ward region of the display device from an image in a linear domain carried by the spatially modulated light beam;

an eye-tracking system for determining an eye pupil position of a display user in the eye-ward region; and

12. The display device of claim 10, wherein the beam redirection module comprises a stack of switchable gratings; alternatively, the process may be carried out in a single-stage,

wherein the stack of switchable gratings comprises a Pancharatnam-Berry phase (PBP) Liquid Crystal (LC) switchable grating; and, further optionally,

wherein the PBP LC switchable grating comprises an LC layer between a plurality of parallel substrates configured to apply an electric field across the LC layer, wherein LC molecules in the LC layer are oriented substantially parallel to the plurality of substrates in the absence of the electric field and substantially perpendicular to the plurality of substrates in the presence of the electric field.

13. A method for displaying an image to a user, the method comprising:

providing a light beam;

receiving and spatially modulating the light beam to provide a spatially modulated light beam carrying an image in the linear domain; and

a beam redirection module is used to variably redirect the spatially modulated light beam toward the user's eye.

14. The method of claim 13, the method further comprising: an image in the angular domain is formed by a vision lens from an image in the linear domain carried by the spatially modulated light beam and redirected by the beam redirecting module, optionally,

Determining an eye pupil position of the display user in the eyebox; and

causing the beam redirection module to redirect the spatially modulated light beam to match the eye pupil position in the eyebox.

15. The method of claim 13, wherein using the beam redirection module comprises switching at least one switchable grating in a stack of switchable gratings.